The Need for Electronic Yarn Clearer
Electronic Yarn Clearer can remove selective yarn faults, taking into consideration all aspects of a fault.
Increase in global competitiveness over the years has led to more and more demands being placed on the quality of yarn being delivered.
Under such circumstances, the conventional method of removal of yarn faults by slub catchers proved to be ineffective.
The deficiencies inherent with the mechanical clearing of faults could be listed as follows:
- Very low Clearing Efficiency ( hardly 30%)
- Inability to remove thin places
- Non-consideration of the fault length
- The necessity of setting the slub catcher at each winding position
- Deterioration in yarn quality by abrasion
- Possibility of tampering of the setting.
All these deficiencies are successfully overcome by ‘ electronic yarn clearing’ where selective removal of faults is possible taking into consideration all aspects of a fault.
Besides, the centralized setting facility enables uniform settings on all winding positions and also eliminates tampering of the setting.
Types of Electronic Yarn Clearer
Electronic Yarn Clearers available in the market are the principle of two types – capacitive and optical.
Clearers working on the capacitive principle have ‘ mass’ as the reference for performing its functions while optical clearers function with ‘ diameter ’as the reference.
Both have their merits and demerits and are equally popular in the textile industry. Besides the above basic difference in measuring principle, the basis of functioning of both the types of clearers is similar if not exactly the same.
Since most of the other textile measurements like U% / CV%, thick and thin places, etc., in various departments, take into account mass as the reference parameter, the functioning of the capacitive clearer is explained in some detail in the following sections.
Functioning Principle of Capacitive Principle
The yarn is measured in a measuring field constituted by a set of parallelly placed capacitor plates.
When the yarn passes through this measuring field (between the capacitor plates), an electrical signal is produced which is proportional to the change in mass per unit length (linear density) of the yarn.
This signal is amplified and fed to the evaluation channels of the yarn clearing installation. The number and type of evaluation channels available are dependent on the sophistication and features of the model of the clearer in use.
Each of the channels reacts to the signals for the corresponding type of yarn fault. When the mass per unit length of the yarn exceeds the threshold limit set for the channel, the cutting device of the yarn clearer cuts the yarn.
Electronic Yarn Clearer Settings
The yarn clearer has to be provided with certain basic information in order to obtain the expected results in terms of clearing objectionable faults. The following are some of them.
a. Clearing Limit
The clearing limit defines the threshold level for the yarn faults, beyond which the cutter is activated to remove the yarn fault. The clearing limit consists of two setting parameters – Sensitivity and Reference Length.
i. Sensitivity – This determines the activating limit for the fault cross-sectional size.
ii. Reference Length – This defines the length of the yarn over which the fault cross – section is to be measured.
Both the above parameters can be set within a wide range of limits depending on specific yarn clearing requirements. Here, it is worth mentioning that the ‘ reference length ’may be lower or higher than the actual ‘ fault length.
For a yarn fault to be cut, the mean value of the yarn fault cross-section has to overstep the set sensitivity for the set reference length.
b. Yarn Count
The setting of the yarn count provides a clearer with the basic information on the mean value of the material being processed to which the clearer compares the instantaneous yarn signals for identifying the seriousness of a fault.
c. Material Number
Besides the yarn count, there are certain other factors which influence the capacitance signal from the measuring field like the type of fibre (Polyester / Cotton / Viscose, etc.) and environmental conditions like relative humidity.
These factors are taken into consideration in the ‘ Material Number’. The material number values for different materials are provided in Table.
From the values given in the table it could be seen that, for water-absorbent fibres like cotton, the Material Number is changed by 1 for a 15% change in Relative Humidity. A reduction in material number results in a more sensitive setting causing higher fault removal.
For blended yarns, the material number is formed from the sum of the percentage components of the blend. For instance, when a 67/33 Polyester / Cotton blend is run at an RH of 65%, the Material Number should be set at (0.67 * 3.5) + (0.33 * 7.5) = 4.8.
d. Winding Speed
The setting of the winding speed is also very critical for accurate removal of faults. It is recommended that, instead of the machine speed, the delivery speed be set by actual calculation after running the yarn for 2-3 minutes and checking the length of yarn delivered.
Setting a higher speed than the actual is likely to result in a higher number of cuts. Similarly a lower speed setting relative to the actual causes fewer cuts with some faults escaping without being cut.
In most of the modern day clearers, the count, material number and speeds are monitored and automatically corrected during the actual running of the yarn.
The various fault channels available in the latest generation yarn clearer are as follows:
- Short Thick places
- Long Thick Places
- Long Thin Places
The availability of one or more of the above channels is dependent on the type of yarn clearer.
Yarn clearers conventionally used on a manual winder have channels only for the short thick places and long thick places with a setting facility for only the short thick places.
However even for the manual winders, clearers are now available like the Micro 2000 Clearers from PREMIER with most of the channels given above.
Besides the detection of the various types of faults, with latest clearers, it is also possible to detect the concentration of faults in a specific length of yarn by means of alarms.
Detection of contamination in normal yarn has become a requirement in recent times due to the demands of yarn buyers abroad.
Therefore, some of the optical yarn clearers have an additional channel to detect the contamination in yarn. This is mostly used while clearing cotton yarn.
The various facilities available in the yarn clearers nowadays enable precise setting and removal of all objectionable faults while at the same time ensure a reasonably high level of productivity.